Document collaboration functionality eval

Use cases:

Collaborative drafting by group moderators of a document with an assessment protocol like for a feasibility study for reef restoration efforts (see example in Test Group). Only experts or group moderators of the IG together draft the document. Once done, it can either stay as-is if it is good enough available to all members of the IG or even complete BBN, or it can be taken and edited into a proper laid-out PDF that is ready for publishing or inclusion in other documents.
Members of an IG all add information on successfull alternative livelyhood projects they have worked on, together with links to further information. This would bundle collective knowledge in one place for all group members to use.
A closed group of for instance an NGO or consultancy firm working on a project or plan that is not meant to be public (yet) can use the document functionality to gather their thoughts and work out a project/product plan collaboratively.

Advantages to alternatives:

Email and facebook: conversation obfuscated with other conversations
Email and facebook: no searching through comments and versions to get to the "current version"
All documents about one topic together. You don't need to search in inbox, FB groups or mailing list archives when something was discussed
Asynchronous: whenever someone has ideas/time they can contribute, while email, FB, mailinglists and fora all have a clear timestamp element on them. You are expected to react when others do.

Existing functionality:

History tracking makes it easy to discuss things and edit without the fear of loosing information
Discussion functionality allow collaborators and (if accessible to them) the general audience able to discuss the document without actually editing it
Simple markup toolbar allows for structural formatting without loosing one-self in layout.
Permissions allow fine-grained access control between group moderators, group members and the general public
Full-screen editing button allows for undistracted working

Desired functionality:

Download as word or odf document
Autosave functionality to prevent loosing changes
A bit neater visual integration to the groups? Maybe remove some clutter/elements to make it neater/simpler? Maybe not important/necessary now (or ever).

Challenges/problems: